Conventionally, a high pressure pump sending a high pressure fuel is provided in a fuel supply device supplying a fuel to an engine. A component, which has a volume for storing the high pressure fuel sent from the high pressure pump, is a fuel rail. Since a pressure in the fuel rail is maintained, the fuel is injected from an injector.
However, a failure of an adjustment valve included in the high pressure pump, for example, may cause an extraordinary high pressure higher than an acceptable range in the fuel rail, and the fuel rail and the injector may be damaged. A high pressure pump including a relief valve, which is opened when a pressure in a fuel rail extraordinarily increases, has been proposed in Patent Document 1 (JP 2009-114868 A). In the high pressure pump described in Patent Document 1, the pressure in the fuel rail can be decreased by opening the relief valve.
In the high pressure pump described in Patent Document 1, the pressure in the fuel rail decreases after the valve member opens the relief valve for a while, and an urging force becomes larger than a force that opens the relief valve. Therefore, the relief valve once opened is closed, and the relief valve is not opened again unless the pressure in the fuel rail increases up to a predetermined value. Consequently, the pressure in the fuel rail may extraordinarily increase again, and accordingly the fuel rail and the injector may be damaged.